The invention concerns an automatic transmission for a motor vehicle. The automatic transmission comprises a hydrodynamical starting element, in particular a torque converter, such that the automatic transmission is connected to the engine of the motor vehicle by way of the hydrodynamical starting element. The hydrodynamical starting element comprises a pump on the engine side and a turbine on the transmission side. The pump of the hydrodynamical starting element is coupled to the engine of the motor vehicle and the turbine of the hydrodynamical starting element is coupled to a transmission input shaft.
From the prior art, such automatic transmissions with a so-termed static disengagement function are already known. The static disengagement function reduces the consumption of the motor vehicle at rest when the drive position of the automatic transmission is engaged. This can happen either if the static disengagement function shifts the automatic transmission from the engaged drive position to a neutral or a parking position or, alternatively, if at least one clutch involved in the force flow is brought to slipping operation when the drive position is engaged.
Automatic transmissions with a static disengagement function are known in particular from DE 42 23 084 A1, DE 44 46 077 C2 and U.S. Pat. No. 5,272,630. According to DE 42 23 084 A1, when the drive position is engaged, the static disengagement function implements static disengagement when, on the one hand, the vehicle's speed is lower than a limiting speed value and when, in addition, a throttle value of an engine throttle valve is, at the same time, smaller than a limiting throttle valve value. If both these criteria are fulfilled simultaneously then, according to DE 42 23 084 A1, static disengagement is implemented. According to DE 44 46 077 C2, static disengagement is implemented when the drive position of the automatic transmission is engaged; in the event that, on the one hand, the vehicle's speed is lower than a limiting speed value and, on the other hand, at the same time a measured brake pressure of a brake system of the motor vehicle is higher than a limiting brake pressure value. In contrast, according to U.S. Pat. No. 5,272,630, static disengagement is implemented when, on the one hand, the vehicle's speed is lower than a limiting speed value and, on the other hand, the engine speed is lower than a limiting engine speed value. If static disengagement is implemented as a function of engine speed, this has the disadvantage that a specific engine speed limiting value has to be established for each automatic transmission depending on the hydrodynamic characteristic of the hydrodynamical starting element and the idling speed. This translates into high application effort and expense.
Starting from the above, the present invention addresses the problem of providing a new type of method for controlling an automatic transmission and a new type of automatic transmission.
This problem is solved by a method for controlling an automatic transmission. According to the invention, as a further initiation criterion, it is tested whether a characteristic parameter of a turbine of a hydrodynamical starting element, in particular a torque converter, is below a limiting value for the characteristic parameter.
In the context of the present invention it is proposed to actuate a standard coupling when, on the one hand, the speed of the motor vehicle is lower than a limiting speed value and when, on the other hand, a characteristic parameter of a turbine of the hydrodynamical starting element is below a limiting value for the characteristic parameter.